The present invention relates to a method and apparatus for forming an insulating film containing silicon oxy-nitride on a silicon layer exposed to the surface of a target substrate.
With micropatterning of semiconductor devices, insulating films used in these devices, e.g., the gate insulating film and the like of a MOSFET are being more and more thinned. Generally, as the film thickness decreases, a silicon oxide film (SiO2 film) readily increases the initial percentage of insulation defect or deteriorates the electrical characteristics such as the dielectric breakdown characteristic with time or the transistor characteristic. Also, in a post-annealing step, boron (B) as a dopant of a p+-polysilicon electrode penetrates to the substrate through the silicon oxide film.
The electrical characteristics thus deteriorate presumably because unbonded hands (dangling bonds) exist in the interface between the oxide film and an underlying silicon film and these dangling bonds are closely related to the electrical film quality of the oxide film. Hence, a method is known which forms an oxide film by oxidizing the surface of a silicon (Si) film and anneals the oxide film at a high temperature in a nitrogen (N2) gas atmosphere or in a gas mixture atmosphere of nitrogen gas and ammonia gas, thereby improving the film quality. This method requires a high temperature of 1,000xc2x0 C. or more to improve the electrical characteristics, so a large heat history accumulation (thermal budget) may occur for the formed film.
On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 5-251428 (Jpn. Patent No. 2793416) has disclosed a method of forming a silicon oxy-nitride film by forming a silicon oxide film by dry-oxidizing a silicon substrate and processing the oxide film with a nitrogen-containing oxidizing gas in a lamp heating type single wafer processing apparatus capable of rapid heating.
More specifically, a silicon substrate is first loaded into a process chamber. While an oxidizing gas not containing nitrogen, e.g., dry oxygen gas (O2 gas) is caused to flow, this silicon substrate is oxidized by heating at about 1,000xc2x0 C., thereby forming a silicon oxide film. The heating of the substrate is rapid heating done at a heating rate of from 50 to 200xc2x0 C./sec by an infrared lamp. The temperature retention time for the oxidation at 1,000xc2x0 C. is set to about 10 sec. Also, the processing pressure for the oxidation is set to about 760 Torr.
Subsequently, with the silicon substrate kept at about 1,000xc2x0 C. in the same process chamber, the process chamber is once evacuated, and the silicon oxide film is processed while an oxidizing gas containing nitrogen is caused to flow into the process chamber. In this manner, the silicon oxide film is converted into a silicon oxy-nitride film. The nitrogen-containing oxidizing gas herein used is at least one gas selected from the group consisting of nitrogen monoxide (NO), nitrogen dioxide (NO2), and dinitrogen monoxide (N2O). The temperature retention time for the oxy-nitriding at 1,000xc2x0 C. is set to about 30 sec. The processing pressure for the oxy-nitriding is set to about 760 Torr.
The method described in Jpn. Pat. Appln. KOKAI Publication No. 5-251428 uses rapid heating. Hence, the method improves the problem of thermal budget as compared to the former method. However, this method is unsuited to the formation of thin films and cannot control the film thickness and the film quality with excellent reproducibility.
It is an object of the present invention to improve the controllability and reproducibility of the film thickness and the film quality (particularly the electrical characteristics) in a technology of forming a thin insulating film at least partially consisting of silicon oxy-nitride.
It is another object of the present invention to provide a method suited to a hot wall type processing apparatus, particularly a vertical heat-treating apparatus for performing batch processing, and an apparatus for practicing the method.
According to a first aspect of the present invention, there is provided a method of forming an insulating film containing silicon oxy-nitride, comprising
a loading step of loading a target substrate into a process chamber, the substrate having a silicon layer exposed to a surface,
an oxidation step of setting an atmosphere in the process chamber at a first heating temperature and a first pressure for a first processing time, and supplying a first processing gas for oxidation into the process chamber to oxidize a surface of the silicon layer, thereby forming a silicon oxide film on the silicon layer, the first processing gas containing 1 to 5 vol % of water vapor and 95 to 99 vol % of nitrogen gas, and
an annealing step of setting the atmosphere in the process chamber at a second heating temperature and a second pressure for a second processing time after the silicon oxide film is formed, and supplying a second processing gas for nitriding into the process chamber to convert at least a portion of the silicon oxide film into silicon oxy-nitride, the second heating temperature being 800 to 950xc2x0 C., and the second processing gas containing 10 to 100 vol % of nitrogen monoxide gas.
According to a second aspect of the present invention, there is provided an apparatus for forming an insulating film containing silicon oxy-nitride on a silicon layer exposed to a surface of a target substrate, comprising
an airtight process chamber,
a holding member for holding the substrate in the process chamber,
a gas supply system for supplying a processing gas into the process chamber,
an exhaust system for vacuum-exhausting the process chamber,
a heater for heating an atmosphere in the process chamber, and
a controller for controlling the gas supply system, the exhaust system, and the heater,
wherein the controller is so arranged as to perform
an oxidation step of setting the atmosphere in the process chamber accommodating the substrate at a first heating temperature and a first pressure for a first processing time, and supplying a first processing gas for oxidation into the process chamber to oxidize a surface of the silicon layer, thereby forming a silicon oxide film on the silicon layer, the first processing gas containing 1 to 5 vol % of water vapor and 95 to 99 vol % of nitrogen gas, and
an annealing step of setting the atmosphere in the process chamber at a second heating temperature and a second pressure for a second processing time after the silicon oxide film is formed, and supplying a second processing gas for nitriding into the process chamber to convert at least a portion of the silicon oxide film into silicon oxy-nitride, the second heating temperature being 800 to 950xc2x0 C., and the second processing gas containing 10 to 100 vol % of nitrogen monoxide gas.
In the present invention, water vapor is used in oxidation. Therefore, it is possible to obtain a wet oxide film having little distortion in the vicinity of the SiO2/Si interface and good electrical characteristics compared to a dry oxide film. In addition, the oxidation rate can be adjusted by mixing nitrogen gas in the water vapor. This can improve the film quality of the wet oxide film and also improve the controllability and reproducibility of the film thickness and the film quality. Note that wet oxidation cannot be used in a cold wall type single wafer processing apparatus using lamp heating, because byproducts such as NHO3 (nitric acid) may be produced.
The wet oxide film is annealed subsequently to the oxidation. In this annealing, the wet oxide film is annealed in an atmosphere containing nitrogen monoxide gas. Hence, nitrogen enters into the SiO2/Si interface, and dangling bonds in this interface terminate by nitrogen of the nitrogen monoxide gas and decrease (i.e., silicon oxy-nitride forms). In this way, the electrical characteristics of the high-quality wet oxide film further improve by the formation of the silicon oxy-nitride.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.